depot_tools: Update README file to point to bootstrap/gclient.sh/.bat instead of bootstrap/update.sh
depot_tools: Update README file to point to bootstrap/gclient.sh/.bat instead of
bootstrap/update.sh

BUG=38130
TEST=None

Review URL: http://codereview.chromium.org/2818011

git-svn-id: bd64dd6fa6f3f0ed0c0666d1018379882b742947@50099 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

svn2github/chromium-depot-tools,svn2github/chromium-depot-tools,svn2github/chromium-depot-tools